light-year

noun

ˈlīt-ˌyir 

1

: a unit of length in astronomy equal to the distance that light travels in one year in a vacuum or about 5.88 trillion miles (9.46 trillion kilometers)

2

: an extremely large measure of comparison (as of distance, time, or quality)

seems like light-years ago

has light-years more talent

two minutes and yet light-years away from the crowded village

—Suzanne Patterson

Synonyms

• world
• galaxy

Examples of light-year in a Sentence

my sister and I are close in age, but personality-wise, there are light-years between us

Recent Examples on the Web

Slightly above it, to the moon’s upper left, lies yellowish Castor, which is about 51 light-years distant. —Jamie Carter, Forbes.com, 14 Sep. 2025

Imagine if the nearest intelligent aliens were not across the street, not across the solar system, but on the far side of the Milky Way, some 33,000 light-years away from Earth. —Rupendra Brahambhatt, Interesting Engineering, 13 Sep. 2025

Stretching across 8 light-years, the rare stellar eruption is about twice the distance between our sun and the next nearest stars. —Eric Lagatta, USA Today, 12 Sep. 2025

This young star is located 15,000 light-years from Earth on the very outskirts of the Milky Way's spiral disk, where the abundance of elements heavier than hydrogen and helium is low. —Keith Cooper, Space.com, 11 Sep. 2025

Word History

First Known Use

1864, in the meaning defined at sense 1

Rhymes for light-year

• atmosphere
• biosphere
• centromere
• chemosphere
• chromosphere
• hemisphere
• hydrosphere
• lithosphere
• mesosphere
• microsphere
• miserere
• mountaineer

Kids Definition

light-year

noun

ˈlīt-ˌyi(ə)r

1

: a unit of length in astronomy equal to the distance that light travels in one year or 5,880,000,000,000 miles (9,460,000,000,000 kilometers)

2

: a very great distance especially in progress

light-years ahead in design